MicroRNA is a small RNA of 18-25 mer, which is transcribed from the genome and regulates expression of the target gene. It is known that abnormal expression of microRNA is deeply involved in many diseases such as cancer and the like, and studies of microRNA as a target of diagnoses and treatments have been strenuously conducted in recent years. A method of inhibiting microRNA includes a method using LNA (Locked Nucleic Acid), and the method is in the clinical phase in Europe and the United States. As other inhibitory method of microRNA, there is a technique called microRNA Sponge (non-patent document 1).